ProSoft Technology MVI56-AFC - Manual (Page 135)

MVI56-AFC ♦ ControlLogix Platform Events
Liquid and Gas Flow Computer User Manual
ProSoft Technology, Inc. Page 135 of 316
February 25, 2011
Completion Phase
This phase commits a session by determining a final FDP for the event log
header, closing the session, and discarding the dynamic context. If the value of
the final FDP differs from its original value in the event log header, then the
header is updated with the new value and, provided that Site Option "Event Log
Locked" is set, the Download event is written. If the FDP has not changed, no
Download event is written, so the download state of the log remains unchanged.
The session is then closed and its dynamic context discarded. The final FDP is
determined by one of two methods:
1 Implicit Completion: Issue a Modbus write of a single register to offset 0 of
the LDW, specifying function "Commit Session" (2) with the correct Session
ID. This method takes the final FDP from the dynamic context at the moment
of completion.
2 Explicit Completion: Issue a Modbus write of two registers to offset 0 of the
LDW, the same as Implicit Completion but passing in the second register the
desired final FDP as an explicit value. If at any time during the session the
FDP of the dynamic context reached this value, this value becomes the final
FDP for the session completion, in preference to that of the dynamic context.
If the explicit FDP was not reached, this phase is equivalent to session
abandonment (next). An Explicit Completion never marks more events as
"downloaded" than an Implicit Completion.
A Completion of either method can implicitly acknowledge the final Fetch
transaction.
Abandonment
This action explicitly abandons a session by closing it and discarding the
dynamic context, without updating the log header or writing a Download event. In
this case, therefore, adjustment of the log’s download state implied by a changed
FDP is not performed. It is equivalent to waiting for the session timeout to occur
except that its effect is immediate. Issue a Modbus write of a single register to
offset 0 of the LDW, specifying function "Abandon Session" (3) with the correct
Session ID.